Referring now to the drawings, conventional electronic part mounting is described below.
FIG. 5 is a perspective view of a conventional electronic part mounting apparatus. The electronic part mounting apparatus is basically composed of an XY table 7 for disposing a substrate thereon and moving in two axial directions (X, Y directions), a parts feed table 6 for mounting an electronic part thereon and feeding in a rotary head drive section, and a rotary head drive section 8 for feeding and mounting an electronic part, and by moving the XY table 7, the substrate is moved to a specified mounting position, the part is supplied into a suction nozzle 5 of the rotary head drive section 8 from the parts feed table 6, and the electronic part is supplied and mounted on the substrate by the suction nozzle 5.
FIG. 4 is a perspective view of the rotary drive section 8 in the conventional electronic part mounting apparatus. A rotary head 1 supplies and mounts electronic parts on a plurality of suction nozzles 5 disposed around the rotary head 1, and a rotary head driving motor 2 intermittently rotates the rotary head 1 through a mechanism (not shown) for converting the continuous rotation of the motor 2 into intermittent rotation. Moreover, the rotary head driving motor 2 is to rotate the rotary head 1 and to move up and down the suction nozzles 5, and by rotating a cam 4 through a timing belt 3, the suction nozzle is moved up and down.
FIG. 3 is a diagram to explain the operation of the rotary head, showing the rotary head 1 having sixteen suction and mounting nozzles 5 as an example.
This rotary head 1 rotates intermittently in the arrow direction in the drawing while stopping at each station indicated by ST1 to ST16 in the drawing. At the seventh station (ST7), the electronic parts are sucked by the suction and mounting nozzles 5, and the electronic parts are mounted at the fifteenth station (ST15). Thus, mounting and suction of electronic parts and rotation of the rotary head are executed alternately.
FIG. 2 is a drawing showing rotational speed curve of the rotary head driving motor, and as shown in the drawing the rotational speed V.sub.L (pulses/s) of the rotary head driving motor 2 is constant during the mounting cycle T. Herein, the rotational speed of the rotary head driving motor is defined to be pulses/s, and the acceleration to be pulses/s.sup.2. The rotary head driving motor is provided with an encoder as an angle detector in the AC servo motor, and driving of the motor is controlled by using a pulse signal from the encoder. (In this example, 1000 pulses of digital signal are issued per revolution of the motor). Hence, the rotational speed V.sub.L can be defined by the number of encoder pulses for driving the motor per second, so that the quantity of rotation and number of revolutions of the motor can be determined.
The mounting cycle is generally the time required for mounting one part, and as shown in FIG. 2 it is the total time T of rotation of rotary head and suction and mounting of part. More specifically, as shown in FIG. 3, it refers to the time from start of move of the suction nozzle 5 of the rotary head until moving to adjacent suction nozzle and starting to move to next place, and for example, it refers to the time required from star of move of ST7 until suction nozzle 5 starts to move to ST8.
Conventionally, the rotational speed V.sub.L is the lower rotational speed of either the rotational speed for sucking and mounting the electronic part stably when the rotary head 1 is stopped, or the rotational speed not changing in the suction posture when the rotary head 1 rotates.
In the prior art, however, the problem was that the mounting cycle T was dominated only by the lower rotational speed of either the rotational speed of the rotary head driving motor 2 for sucking and mounting stably when the rotary head 1 is stopped, or the rotational speed of the rotary head driving motor 2 not causing change in suction posture when the rotary head 1 rotates. Accordingly, the electronic parts could not be mounted efficiently hitherto.